All distance measuring devices measure the distance between two points. One type of hand-held distance measuring device uses the round trip transit time of projected energy to a target and back to the device to determine distance.
Although this type of hand held measuring device works, it has some problems. One of the problems with this type of device is with establishing a reference plane from which the measurements are made. Errors in establishing the correct reference plane result in measurement errors. Another problem is that this type of hand held measuring device requires the user to manually turn the device on, as well as enter other measurement parameters, before being able to perform the distance measurement.